Synthesis and properties of polyimides derived from 2,2′-dichloro-4,4′,5,5′-biphenyltetracarboxylic dianhydride

To investigate the effect of introducing 2,2′-dichloro substituted biphenyl linkage into the polymer backbones on the properties of polyimides (PI), 2,2′-dichloro-4,4′,5,5′-biphenyltetracarboxylic dianhydride (DCBPDA) was polymerized with aromatic diamines, including 2,2′-bis(trifluoromethyl)benzidine (TFMB) in m-cresol to obtain a series of soluble polyimides. For comparison, PI without 2,2′-dichloro substitution was prepared derived from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA). The inherent viscosities of the DCBPDA derived polyimides were tested in the range of 0.88–2.14 dL g−1. Thermal analysis revealed DCBPDA type polyimides had coefficients of thermal expansion in the range of 15.1–29.5 ppm.K−1. Their glass transition temperatures were in the range of 355 °C–437 °C, and were higher than the BPDA derived counterpart. Additionally, the employment of DCBPDA resulted in better organo solubility and optical transparency. For example, PI(DCBPDA/TFMB) could be dissolved in acetone and ethyl acetate at room temperature, the film showed a transparent and colorless feature. The results were analyzed from the perspective of structure-property relationship, and may provide helpful knowledge for the topic of polyimide chemistry.